This application relates generally to gas turbine engines and, more particularly, to methods to facilitate extending the useful life and/or the reliability of gas turbine engines.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. These same standards have caused turbine engine manufacturers to design more efficient engines, as well as design improved retrofit components that enable engines to operate more efficiently, with improved emissions, and/or with extended useful life and reliability. Moreover, the generally high capital costs associated with the purchase and maintenance of turbine engines, such as revenue losses generated during engine outages, have caused the same engine manufacturers to attempt to design engines that are more reliable and that have extended useful life.
Known turbine engines include a compressor for compressing air which is mixed with a fuel and channeled to a combustor wherein the mixture is ignited within a combustion chamber for generating hot combustion gases. At least some known combustors include a dome assembly, a bolt banding, and liners to channel the combustion gases to a turbine. The turbine extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator. The liners are coupled to the dome assembly at an upstream end with the bolt banding, and extend downstream from the bolt banding to define the combustion chamber.
Generally, assets, such as turbine engines, are subject to failure by two types of causes. Wear, which is highly correlated to operating hours (engine flight hours) or cyclic operation, and thermal shock, which is highly correlated to start events (engine cycles). Specifically, during engine operation, the combustor and the turbine are exposed to high temperatures which may induce thermal stresses within the combustor and/or the turbine. Over time, continued operation with thermal stresses may cause portions of the combustor and/or turbine thermally fatigue, causing material erosion, weakening, oxidation, and/or cracking to develop within such components.
To detect failed components as a result of wear and/or thermal shock, generally a determination to assess the mode more probable to cause failure of the asset is made and the mission (hours per cycle or flight leg for an aircraft engine) is selected to balance the failure modes, increasing the utilization of the life built into the engine. Known engine manufacturers then select pre-determined intervals at which time the engines are removed and newer engines are installed, or portions of the engine are inspected to determine if specific components, such as the combustor liner, are distressed or beyond serviceable limits, thus warranting repair or replacement. However, replacing engines without inspection generally results in sacrificing at least a portion of the useful life of the engine, while the combination of the inspections of engine components at pre-determined intervals in combination with necessary repairs and/or replacement installations, may be a costly and time-consuming process that adversely impacts the operational availability of such engines.